Optimizing the Stimulus to Maximize System Performance

1

• Optimizing the Stimulus to Maximize System
  Performance

2
Agenda

• Agenda

• Overview
• System functionality test and troubleshooting
• Amplifier test
• Frequency conversion system test considerations
• Baseband system test considerations
• Summary

3
Overview

• Superheterodyne radio architecture

TRANSMITTER
I
Digital signal processor/FPGA
x
DAC
IF Filter
Filter
FIR
0 deg
x

Symbol Encoder
IF LO
90 deg
Q
x
DAC
FIR
Filter
RF LO
Baseband
Frequency conversion
Amplification
I
Digital signal processor/FPGA
RECEIVER
x
Preselecting filter
ADC
IF FILTER
Filter
0 deg
FIR
x
Symbol Decoder
Decoder
LNA
IF LO
90 deg
ADC
Q
x
FIR
Filter
RF LO
Baseband
Amplification
Frequency conversion
4
Overview

• Receiver architecture progression

RF
IF
Baseband
Superheterodyne
DSP
IF LO
RF LO
Digital
Analog
Direct digital conversion
RF
Baseband
Zero IF
DSP
DAC
RF LO
Baseband to RF
Digital
Analog
DSP
Digital
Analog
5
Overview

• Common stimuli test points

TRANSMITTER
I
Digital signal processor/FPGA
2
1
x
DAC
IF Filter
Filter
FIR
4
0 deg
3
x

Symbol Encoder
IF LO
90 deg
2
1
x
DAC
FIR
Filter
Q
RF LO
8
I
Digital signal processor/FPGA
RECEIVER
9
x
Preselecting filter
ADC
IF FILTER
Filter
FIR
0 deg
7
x
Symbol Decoder
Decoder
LNA
5
IF LO
9
6
90 deg
ADC
Q
x
FIR
Filter
8
RF LO
Denotes test points
6
System Functionality Test Troubleshooting

• Agenda

Frequency conversion section
Baseband section
Amplification section

• Overview
• System functionality test troubleshooting
• Amplifier test
• Frequency conversion system test considerations
• Baseband system test considerations
• Summary

7
System Functionality Test Troubleshooting

• What is system functionality test ?

Fading
Transmitter
Receiver
transmission channel
BER/PER analysis
Interferers
8
System Functionality Test Troubleshooting

• Why is system functionality testing important?

• WLAN cards are inexpensive
• Rework increases price
• Perfect quality is expected

• Satellites are expensive
• Rework may not be possible
• A/D applications must be reliable

9
System Functionality Test Troubleshooting

• How to perform system functionality tests

Field test
Commercial fader
DUT (Rx)
DUT (Rx)
Record the test signal play it back
DUT (Rx)
Record
Play back
10
System Functionality Test Troubleshooting

• Field trial considerations

Advantages

• Real operational conditions

Disadvantages

• Expensive
• Inefficient
• Non-repeatable
• Limited cannot cycle through full range of
  conditions
• Rework may not be possible

11
System Functionality Test Troubleshooting

• Fading considerations

Multiple RF/MW channels
Multiple RF/MW channels
Fading Profiles Multiple Paths
Required bandwidth increases as the number
of paths increase
12
System Functionality Test Troubleshooting

• Waveform recording streaming considerations

• Memory depth
• Impacts recording time (signal analyzer)
• Impacts play back time (PC and signal generator)
• Converter Resolution
• Impacts quantization noise, fidelity, and dynamic
  range
• Signal analyzers ADCs
• Signal generators DACs
• Bandwidth
• Wide enough for capture playback

Amplitude
Sample time
Amplitude
Frequency
13
Amplifier Test

• Agenda

Amplification section

• Overview
• System functionality test and troubleshooting
• Amplifier test
• Frequency conversion system considerations
• Baseband system considerations
• Summary

Frequency conversion section
Baseband section
Amplification section
14
Why is amplifier characterization important?
Amplifier Test
In-channel distortion
PowerOut
PowerIn
Amplitude
Amplitude
Amplifier
Frequency
Frequency
Out-of-channel distortion
15
Amplifier Test

• How to characterize nonlinear distortion

16
Amplifier Test

• Test narrow band components

In-band
Two-tone
TOI IMD
2f2-f1
2f1- f2
Amplitude
. . .
f2
f1
f1
f2
Frequency
3rd order IMD
17
Test broad band components
Amplifier Test
Multitone test
Noise power ratio test
Amplitude
Amplitude
Frequency
Frequency
Out-of-band tests
In-band tests
18
Amplifier Test
Complementary cumulative distribution curves
AWGN (reference)
Before Non-compressed signal
Probability
After Compressed signal from distortion
Peak/Average dB
19
Amplifier Test

• Multitone phase relationship impacts CCDF

Equal phase set crest factor 17.88 dB
Random phase set crest-factor 6.70 dB
20
Multitone test setup CW sources
Amplifier Test
1 CW source needed for each tone
Spectrum analyzer
CW source
LPF
Isolator
AMP

CW source
Combiner

CW source

Denotes isolators
21
Multitone test considerations CW sources
Amplifier Test
Advantages

• Established test procedure
• Common test equipment

Disadvantages

• Complicated test setup
• Time-consuming to change signal parameters
• Difficult to generate repeatable random tones
• Expensive

22
Multitone test setup vector signal generator
Amplifier Test
1 vector signal generator creates many tones

• Reduce cost
• Simplify test procedure
• Save time
• Repeatable test setup
• Accurate test results
• Control signal parameters
• Utilize digital predistortion (DPD) capabilities
  of the multitione signal creation software

Vector signal generator
Spectrum analyzer
23
Multitone example
Amplifier Test
Signal Studio for enhanced multitone software
Minimize test stimulus IMD even at the output
of an external power amplifier!
Low IMD reduces test uncertainty
Vector signal generator
IMD products from DUT
Spectrum analyzer
Non-linear distortion measurement
24
Amplifier Test

• Before after digital predistortion

25 dB improvement
Before
and After
25
Amplifier Test

• Images

Images resulting from I/Q skew
Minimize images by adjusting the I/Q skew
26
Multitone test considerations vector signal
generator
Amplifier Test
Advantages

• Simple test setup and procedure
• Easy to modify signal parameters
• Improved signal quality
• Repeatable and accurate test results
• Save time and test equipment cost

Disadvantages

• Output power distributed
• Carrier feedthrough

27
Amplifier Test
What is noise power ratio (NPR)?
Noise Stimulus
DUT
Amplitude
Amplitude
Frequency
Frequency
Notch
Noise generated By DUT
28
NPR test setup CW and noise source
Amplifier Test
NPR stimulus requirements
Band Stop Filter
Up converter
Noise Source
IF
RF
LO
CW source
Spectrum analyzer
29
NPR test setup vector signal generator
Amplifier Test
NPR stimulus requirements
LAN or GPIB
Vector signal generator
Signal Studio for NPR software

• Save time with simplified test setup
• Accurate test results
• Movable notch without analog filters
• Better dynamic range
• Repeatable results
• Phase and CCDF

Spectrum analyzer
30
Advantages of pseudo-random tones over analog
noise
Amplifier Test
Analog noise
Pseudo-random tones
Better dynamic range
Amplitude
Amplitude
Frequency
Frequency

• Better signal-to-noise ratio
• Steeper filter
• Flatter amplitude

31
Amplifier Test

• Complex stimulus/response

Digitally modulated single and multicarrier
ACPR, SEM, EVM
PowerIn
PowerOut
Amplitude
Amplitude
Amplifier
Frequency
Frequency
32
Amplifier Test
Timing and phase offsets impacts the crest factor
AWGN signal (used as a reference)
Multicarrier W-CDMA with no offsets applied
18 dB crest factor!

• Apply timing phase offsets for CDMA
• Randomize code channels for CDMA
• Apply phase offsets for multicarrier

33
Amplifier Test
Use clipping to limit the signal peaks
Signal after clipping
Signal before clipping
Gaussian noise
34
Common techniques to clip waveforms
Amplifier Test
Rectangular Clipping
Circular Clipping
Peak power without clipping (clipping set to 100)
Peak power without clipping
Vector representation of clipped I Q
I waveform
Baseband waveform
Vector representation of clipped peak
Clipping set to 80
Clipping applied
Q waveform
35
Frequency Conversion System

• Agenda

Frequency conversion section
Amplification section

• Overview
• System functionality test and troubleshooting
• Amplifier test
• Frequency conversion system considerations
• Baseband system test considerations
• Summary

Frequency conversion section
Baseband section
Amplification section
36
Frequency Conversion System
Frequency conversion system impacts measurements
Vector signal generator
Amplification section
Baseband section
Level accuracy Spectral Purity Bandwidth
Baseband section
Amplification section
Vector signal generator
37
What is level accuracy?
Frequency Conversion System
1
2
Absolute Amplitude (dBm)
Repeatability (dB)
-10 dBm
-10 dBm
A
B
Amplitude
Amplitude
f1
f1
f2
Frequency
Frequency
3
4
Relative level accuracy (dB)
Linearity (dB)
-10 dBm
1 dB
Amplitude
Amplitude
24 dB
Amplitude
-100 dBm
Frequency
f1
Frequency
f1
Attenuator hold on
Frequency
38
Frequency Conversion System

• Why is level accuracy important?

-110dBm spec.
-110dBm spec.
-110.5dBm actual
-111dBm setting
Power Output
Power Output
-114dBm actual
-115dBm setting
Frequency
Frequency
Case 1 Source has /-5 dB of output power
accuracy.
Case 2 Source has /-1 dB of output power
accuracy.

Passes test
Should pass but fails
Fails test
39
Frequency Conversion System

• What impacts level accuracy?

• Automatic level control (ALC)
• Flatness
• Crest factor

Power
Flatness
Frequency
Entire frequency range
40
Frequency Conversion System

• How to control level accuracy?

ALC/Burst Modulator
Output Attenuator

• For non-bursted signals
• Use the ALC
• For bursted signals
• Use ALC hold
• Use ALC hold with RF blanking
• Use power search

from frequency conversion section
ALC Driver
ALC Detector
41
Frequency Conversion System

• ALC considerations

• ALC degrades EVM
• Depends on loop bandwidth chosen and bandwidth of
  modulated signal
• ALC detector bandwidth
• smaller than what it is trying to detect,
  otherwise level accuracy suffers

ALC BW 100 Hz
The smaller the ALC BW, the less it impacts EVM
ALC BW 10 kHz
ALC BW 1 kHz
Amplitude
Modulated signal
frequency
42
Frequency Conversion System

• Level control for bursted signals using the ALC

Bursted signal
1
Amplitude, V
time
ALC on ALC will try to correct the power of the
off period
RF power envelope of the bursted signal
2
Power, dBm
Average power
time
Marker
ALC is on during this time
Logic level
3
ALC hold ALC power is held for this duration
time
Pulse/RF blank ALC is held for this duration
and the RF output is blanked, thus resulting in a
greater on/off ratio
Marker route to ALC hold or Pulse/RF blank
43
Frequency Conversion System

• Power flatness affects accuracy of wideband
  signals

As bandwidth increases, the more power flatness
impacts level accuracy
BW200 MHz
f12500
f22700
44
Frequency Conversion System

• Flatness varies by frequency I/Q source type

Absolute level accuracy
Flatness
Power
Frequency
Entire frequency range
45
Frequency Conversion System

• How level accuracy is impacted by the crest factor

Crest factor 10.5 dB
Peak power 13 dBm
Average (RMS) power 23.5 dBM
Amplitude
time
46
Frequency Conversion System

• What is spectral purity?

Harmonic Spur
CW signal
Phase Noise
Non-Harmonic Spur
Amplitude
Broadband noise
f0
2f0
frequency
Phase noise is expressed as jitter in the time
domain
Amplitude
time
47
Frequency Conversion System

• Why is phase noise important?

Channel Separation
Impacts ACPR tests
Adjacent Channel
Amplitude
Phase noise
frequency
Blocking signal
Impacts blocking tests
Amplitude
Desired signal
Phase noise
frequency
48
Frequency Conversion System

• Phase noise degrades signal quality

Phase Noise
I
Test
Signal
Error Vector
Q
f
Ideal Signal
??RMS
Phase Error
Constellation
Phase noise results in rotation of the
constellation
49
Frequency Conversion System

• Phase noise versus offset frequency from carrier

4
10
ó
A
-
ô
7
-
C
10
B
f
10
d
9.9
10


ô
õ
2
10
7
10

ó









4
ô
10
-70
10
6
-
-
f
10
ô
d
6.868
10


A
f
ô
B
õ
4
10
10 dB/decade
L(f) ,SSB phase noise (dBc,/Hz)
-100
D
Digital modulation on
30 dB/decade
CW only
C
-130
-140
20 dB/decade
107
106
105
104
103
102
10
Frequency, offset from carrier
50
Frequency Conversion System

• What does the sources phase noise do to my
  signal?

f2
½
??RMS
??RMS ( ? 2L(f) df )
radians
(9.87 x 10-2 )
?
f1
Root mean square angular deviation
-70







A
B
Test Signal
L(f) ,SSB phase noise (dBc,/Hz)
-100
Error Vector
ideal low pass filter
f
Ideal Signal
??RMS
-140
104
102
10
106
105
103
Frequency, offset from carrier
51
Frequency Conversion System
What improves phase noise performance?

• Multiple cascaded phase locked loops
• PLLs oscillator
• YIG or VCO
• Reference oscillator
• TCXO or OCXO

1 phase locked loop
30 dB improvement
Phase locked loop
Frac-N
Multiple phase locked loops
1 GHz Ref
f
Phase Detector
Primary Oscillator
Reference Oscillator
52
Frequency Conversion System

• Harmonics non-harmonics

• Contributes to distortion
• ACPR dominated by distortion products
• Reported on data sheet as a single value for a
  particular frequency range

Distortion products contribute to ACPR
53
Frequency Conversion System

• Why is bandwidth important?

Example enough bandwidth to transmit 3rd , 5th
order distortion products for a 20MHz wide 4
carrier W-CDMA signal 100 MHz
54
Frequency Conversion System

• What is bandwidth?

RF bandwidth
Baseband bandwidth
Amplitude
-20 MHz
20 MHz
0 Hz
frequency
3 dB bandwidth
40 MHz occupied bandwidth
55
Baseband System

• Agenda

Frequency conversion section
Amplification section
Baseband section

• Overview
• System functionality test and troubleshooting
• Amplifier test
• Frequency conversion system test considerations
• Baseband system test considerations
• Summary

RF system
RF system
Frequency conversion section
Baseband section
Amplification section
56
Baseband System
What is needed from the test equipment?
3
Clock source
Sample clock
4
Data format
ADC
FPGAs, DSPs, ASICS
ADC
Memory
Bus configuration
5
Mechanical connection
2
6
Logic type
1
Stimulus requirements
57
Baseband System

• Stimuli provided by various baseband generators

• Function generator
• simple test stimulus
• sinusoid, ramp, pulse, triangle
• Pattern generator
• pseudo-random bit patterns
• custom data pattern
• Waveform generator
• Complex real-world test stimulus

1
Stimulus requirements
58
Baseband System

• Waveform generators

Real-time generation

• Two types of waveform generators
• Real-time baseband generator
• Arbitrary waveform generator (AWG or arb)

Waveform generated
Waveform played in real-time
Waveform generation with an arb
Compact disc
Waveform generated
Waveform stored to memory
Waveform played back from storage medium
59
Baseband System

• Waveform generator hardware considerations

• Bandwidth wide enough to transmit
• desired signal
• 3rd and 5th harmonics
• Waveform play back memory
• Enough to play back desired signal
• Waveform storage memory
• Large enough to conveniently store your test
  signals

60
Baseband System

• Signal creation software considerations

• Waveform signal creation
• Commercially available software
• Create your own waveform

61
Baseband System

• Test the baseband system with a complex stimulus

Transmitter test
Vector signal generator

• Test the baseband system with the same complex
  stimulus used by the RF system
• Identify baseband problems before RF integration
• Avoid costly rework
• Reduce uncertainty
• Use same test equipment for baseband RF tests

RF system
Digital inputs
Receiver test
Vector signal generator
RF system
Digital outputs
62
Baseband System
Complex stimulus versus PRBS
W-CDMA test signal
PRBS signal (supplied by pattern generator)
18 dB crest factor!
63
Baseband System
Data integrity
2
Mechanical connection

• Mechanical connection
• Short interconnect
• Variety of break-out-boards

Digital outputs
Vector signal generator

Variety of break-out boards
Short interconnect cable
64
Baseband System
Flexible clocking
3
Clock source

• Clock source
• Provides timing between clock data
• Need to adjust for any skew
• Need a variety of clock sources available
• From device under test, test equipment, or other
  clock source

Skew adjustments are needed to meet sample and
hold criteria of device
65
Baseband System
Adaptability

• Data format
• 2s complement, offset binary, 4-16 bit word
  size, MSB, LSB
• Bus configuration
• Serial, parallel
• Logic type
• TTL, CMOS, LVDS
• Configurable test equipment
• Flexible enough to test current future designs

4
Data format
5
Bus configuration
Logic type
6
66
Conclusion
Summary
Optimizing the Stimulus to Maximize System
Performance

• Realistic stimulus helps to ensure your radio
  will work in in its operating environment
• Stimulus requirements have changed for amplifiers
• Traditional specifications are different for
  digital modulation
• Digital baseband system needs a complex stimulus
• Agilent has flexible test equipment to meet all
  your stimulus needs

67
Agilents Vector Signal Generators

• RF and Microwave Vector Signal Generation

• E4438C ESG Vector signal generator
• Frequency to 6 GHz
• Bandwidth up to 160 MHz
• E8267C PSG Vector signal generator
• Frequency up to 20 GHz
• Bandwidth up to 1 GHz
• For Further Information
• www.agilent.com/find/esg
• www.agilent.com/find/psg

68
Agilent Baseband Studio

• N5110A Baseband Studio
  for waveform streaming
• Virtually unlimited playback memory
• N5115A Baseband Studio for fading
• Optimize number of paths versus bandwidth
• Up to 48 paths or 30 MHz bandwidth
• N5102A Baseband Studio digital signal interface
  module
• Digital I/Q digital IF output
• Extremely flexible
• For Further Information
• www.agilent.com/find/basband studio

69

• Thank You for Attending

70
References

• 1 RF Source Basics CD 5980-2060EE
• 2 Digital Modulation in Communications - An
  Introduction application note 1298 
  5965-7160E
• 3 Characterizing Digitally Modulated Signals
  with CCDF Curves application note
  5968-6875E
• 4 Agilent Signal Generator Spectral Purity
  application Note 388 5952-2019